In an exposure process of a semiconductor manufacturing process, an apparatus is used, such as a spin coater or a developer, which treats a semiconductor wafer with rotation.
Such an apparatus is shown in FIG. 6, which is a cross sectional view of certain component parts of an apparatus 100.
A support portion 106 which supports a semiconductor wafer 104 using a vacuum chuck is located in a cylindrical container 102. A nozzle 108 is arranged above the semiconductor wafer 104 so that a solution is applied to a surface 104a of the semiconductor wafer 104. When the solutions is dropped on the surface 104a, the semiconductor wafer 104 is rotated by the support portion 106. Thereby, the solution is uniformly distributed over the surface 104a. 
However, as the wafer 104 is rotated at a high speed, friction occurs between the surface 104a and the dropped solution. Static electricity is generated by this friction and the surface 104a becomes positively charged. An atmosphere above the semiconductor wafer 104 is negatively charged, as shown in FIG. 6.
According to the publication entitled “BREAK THROUGH”, by Dr. Ohmi at Tohoku University, which was published in April, 1993 (Table-1 at p.26), when a resist was applied to a surface of a semiconductor wafer using a similar apparatus, the surface was positively charged at 3000V or more.
Therefore, transistors in the semiconductor wafer might be destroyed and small particles might attach on the surface as a result of the static electricity, which in turn may lead to a reduced throughput and quality. Further, the finer the patterns on the semiconductor wafer, the greater the influence of the static electricity or devices of the semiconductor wafer.